A light emitting device using a light-emitting diode (LED) is widely used for lighting devices such as a backlight for a liquid crystal display device, a signal device, a switch, a lamp for vehicle, and a general lighting. In particular, a white light emitting LED lamp (white LED lamp) in which the LED and a phosphor are combined is focused as an alternate of a lighting fixture using an incandescent lamp and a fluorescent lamp in addition to the backlight of the liquid crystal display device, the lamp for vehicle and so on, and it is translated into practical applications as a white lighting fixture.
An LED lamp in which a blue light emitting LED chip and a yellow phosphor (YAG and so on) are combined and an LED lamp in which a near-ultraviolet light emitting LED chip of which light emitting wavelength is approximately 360 nm to 440 nm and a mixture of respective phosphors of blue, green, red (BGR phosphor) are combined are known as the white LED lamp. In the latter white LED lamp, a phosphor layer is formed by dispersing the phosphor in a transparent resin sealing the LED chip, and a visible light with a desired color such as a white light is obtained by converting near-ultraviolet light emitted from the LED chip into a longer-wavelength light by the phosphor.
The white LED lamp using the latter near-ultraviolet light emitting LED chip is excellent in color reproducibility and a color rendering property compared to the former one, but there is a weakness in inferior to light emission efficiency. There are some reasons in which the LED lamp as stated above becomes disadvantageous in the light emission efficiency, and a film thickness of the phosphor layer is thick can be cited as one of the reasons. The near-ultraviolet light emitted from the LED chip has energy stronger than the visible light, and there is a possibility in which peripheral parts such as a resin constituting the LED lamp are deteriorated. Besides, there is a possibility in which a human body and so on suffers adverse effect if the near-ultraviolet light leaks out of the LED lamp. Accordingly, the thickness of the phosphor layer made up of the transparent resin and the phosphor is made enough thick so that the phosphor absorbs the near-ultraviolet light emitted from the LED chip as much as possible.
A structure in which a substrate and a reflector are combined prevails in the LED lamp, but a probability becomes high in which the visible light emitted from the phosphor is returned to the phosphor layer reflected by the reflector if the reflector exists near the phosphor layer. The visible light returned to the phosphor layer is lost by multiple light reflection of phosphor particles with each other, and therefore, it is a disadvantageous structure from a point of view of the light emission efficiency. Application of a lamp structure in which the reflector is not provided to reduce the loss caused by the multiple light reflection has been studied. According to an LED lamp in which only the LED chip and the phosphor layer covering the LED chip are disposed on the substrate, it is possible to draw the light from not only an upper part but also a side surface of the phosphor layer, and therefore, the light emission efficiency is able to be increased. In the LED lamp excluding the reflector, it is desired to improve adhesion strength between the transparent resin constituting the phosphor layer and the substrate.